Discontinuity among the different networks arises as a severe issue in HetNet. To support the interoperability among the networks, seamless connectivity may be a key challenge and it is desired to be realized to achieve the full benefit of the HetNet. When a UE is moving out from the coverage area of a currently connecting cell (which may be referred to as serving cell), the UE may need to detach from the serving cell and reattach to another cell (which may be referred to as target cell). This procedure may be referred to as a handover (HO). The serving cell sends a HO command to UE. If the UE fails to obtain the HO command, HO failure (HOF) happens. Therefore, seamless mobility is one of the most important requirements for HetNet.